One of the little bombshells dropped from the Verizon Galaxy Nexus training materials concerns NFC and the swappable battery. Because the NFC chip resides on the battery itself, the hardware changes when you change the battery. Not only does your replacement battery have to have NFC capabilities, but the system and NFC chip use a token to match things together for security. We're speculating that ISIS requires this sort of extra layer, but that's just an educated guess. Note that this doesn't mean things won't work, Verizon simply says:
Customers attempting to use more than one battery with the Galaxy Nexus may have less than an optimal experience since the NFC chip within the battery must register a token between the device and the battery each time the battery is swapped.
Less than optimal may mean different things to different people, so this may mean that it takes a bit longer for the system to initialize, NFC settings will need adjusted, not all apps will work properly, or the whole enchilada may not work. We'll know more when the Verizon version hits the shelves. Hopefully, that's soon.
Thanks, +Butch Yon for the heads up!